A153803 - OEIS

%I #7 Dec 24 2016 11:34:36

%S 0,0,0,0,0,2,6,10,49,103,122,167

%N a(n) = A153800(n) - A000043(n).

%t a007691[m_] := Block[{f = 0, i = 1}, While[f < m, If[Divisible[DivisorSigma[1, i], i], ++f]; ++i;]; Return[i - 1]]

%t a153800[n_] := Block[{i = 2, j, f = 0}, While[f < n, j = a007691[i]; If[PerfectNumberQ[j], ++f;]; ++i]; Return[i - 1]]

%t a[n_] := a153800[n] - MersennePrimeExponent[n]

%t a /@ Range[1, 4] (* _Julien Kluge_, Dec 15 2016 *)

%Y Cf. A000040, A000043, A000668, A000225, A000396, A007691, A153800, A153801, A153802.

%K more,nonn

%O 1,6

%A _Omar E. Pol_, Jan 13 2009